Condensed room temperature vulcanized silicone rubber requires the addition of fillers for reinforcement in order to have practical value. Therefore, the type, specific surface area, particle size, surface activity, and amount of fillers all have a certain impact on the reinforcement effect of silicone rubber.
There are various chemical and physical interactions between polysiloxane molecules, fillers, and between polysiloxane molecules and fillers in the reinforced silicone rubber, which significantly improves the performance of the silicone rubber.
Common reinforcing fillers include gas-phase white carbon black, precipitation white carbon black, and calcium carbonate (CaCO3). Lightweight CaCO3 is generally used as a semi reinforcing filler; With the development of nanotechnology, the particle size of active CaCO3 has reached the nanometer level and has some excellent properties that can endow products with certain special properties (such as reinforcement, transparency, thixotropy, and leveling). It can be used as a reinforcing filler for silicone rubber, and its reinforcing effect is comparable to that of white carbon black.
There are usually two methods for surface treatment of fillers using silane coupling agents: ① adding coupling agents during the preparation of modified fillers to turn them into active fillers; ② Add coupling agent and filler together into the rubber compound. The modification of fillers with silane coupling agents using the first method yields better treatment efficiency than the second method.
Different amounts of organic silane coupling agent treated CaCO3 have different effects on the performance of silicone rubber sealant. When the amount of silane coupling agent is around 1.5%, the CaCO3 treated has a better strengthening effect on the sealant. This is because the better the compatibility between CaCO3 and silicone rubber, the greater the strength, elongation at break, and ductility of the sealant.
In the modified CaCO3 reinforced sealant system, the treatment of CaCO3 surface by organic silicon coupling agent will affect the relevant properties of the final sealant. The modification method of using silane coupling agent to pre treat the surface of CaCO3 is better.
In the modified CaCO3 reinforced sealant system, the type of silane has a certain influence on the reinforcement effect of modified CaCO3. Therefore, when modifying calcium carbonate, appropriate types of coupling agents should be selected.
